The invention relates to a screw capper which engages a cap held by a capping head around the threaded mouth of a vessel and tightens it.
A screw capper is widely used for engaging and tightening threads formed on the internal surface of a cap which is held by a capping head with threads formed around the mouth of vessel while the vessels are conveyed in the rotating condition as they are supported by vessel support members which are mounted on a revolving body, by causing a capping head which holds a cap which is formed with internal threads to rotate while moving down.
When tightening the cap by the capping head, if the cap is allowed to rotate together with the cap, a torque which is sufficient to tighten the cap around the mouth of the vessel is not obtained, leaving the likelihood of a liquid leak subsequently. In order to prevent the vessel from rotating when the cap is tightened around it, a capping operation usually takes place while firmly gripping the barrel of a vessel for high rigidity vessels such as glass bottles. However, vessels which are formed of pliable materials such as PET bottles which find an extensive application recently, there arises a likelihood that when the barrel is gripped, the vessel may be deformed to cause a liquid which is filled therein to spill through the mouth of the vessel. Accordingly, there is a proposal for a screw capper (see Japanese Patent Publication No. 36,957/1992) which is capable of preventing a vessel, formed of a pliant material such as PET vessel, from rotating during a tightening operation by the screw capper.
In the screw capper disclosed in the cited Publication, a star-wheel (suspension mechanism 5) is formed with an engaging disc-like projection (anti-rotation blade 6) at a position which bears against the lower surface of a flange on a plastics vessel 1 so that the engagement of the blade with the lower surface of the flange prevents the vessel from rotating. However, with this arrangement, when a vessel is introduced into the star-wheel or when it is discharged from the star-wheel, the lower surface of the flange may be scarred. In particular, during the capping operation when the cap is strongly urged against the vessel by the capping head to cause the flange to engage the disc-like projection, the lower surface of the flange may be seriously scarred if it is attempted to take the vessel out of the star-wheel to be discharged subsequent to the capping operation.
For this reason, in the screw capper disclosed in the cited Publication, upon completion of the capping operation, the bottom of the vessel is placed on a stationary skewed plate to push it up in a gradual manner, thus disengaging the flange from the engaging disc-like projection before the vessel is taken out. However, this arrangement in which the vessel is caused to slide up the skewed stationary plate in order to allow the flange of the vessel to be disengaged from the star-wheel has a drawback that the conveyance of vessels may become unstable.
Accordingly, it is an object of the present invention to provide a screw capper which is free from the likelihood of scarring the lower surface of a flange of a vessel when the vessel is introduced into and discharged from the capper and which is capable of assuring a stable conveyance of vessels upon completion of the capping operation when the lower surface of the flange is to be disengaged from the engaging projection.
Above object is accomplished by a screw capper comprising conveying means including a plurality of support members, each capable of bearing against the lower surface of a flange formed around the mouth of a vessel, thus conveying the vessels while they are suspended by the support members, a capping head for threadably engaging and tightening a cap around the vessel which is being conveyed while it is suspended by the conveying means, and an engaging projection formed on the top surface of the support member and engageable with the lower surface of the flange, the arrangement being such that during the tightening operation of the cap, the capping head operates to depress the vessel through the cap to cause the lower surface of the flange to be engaged with the engaging projection in order to prevent the vessel from rotating. In accordance with the invention, the screw capper further comprises a receptacle member on which the vessel can be placed, and elevating means for elevating the support member, the arrangement being such that upon completion of tightening the cap around the vessel, the support member is caused to move down in order to place the vessel on the receptacle member, thus terminating the engagement of flange with the engaging projection.
With the screw capper constructed in the manner mentioned above, the vessel is discharged after the flange of the vessel is disengaged from the engaging projection by causing the support member to move down upon completion of the capping operation, thus avoiding the likelihood of scarring the vessel by the engaging projection. In addition, the flange of the vessel can be disengaged from the engaging projection in a reliable manner by causing the support member to descend to a location above the receptacle member before the vessel is discharged.
According to an invention the likelihood of the flange of the vessel being scarred by an engaging projection on a gripper is avoided when introducing the vessel into the screw capper. At this end, the support member comprises a gripper which grips a portion located below the flange of the vessel, and when conveying means receives the vessel, the gripper maintains a clearance with respect to the lower surface of the flange while gripping the vessel.
According to an invention, there is provided a screw capper which assures a stable conveyance of vessels when the lower surface of the flange is disengaged from the engaging projection upon completion of the capping operation. This object is accomplished by causing the receptacle member to move in substantially in the same direction and with a same speed as the vessel being conveyed at least in a region where the support member moves down to place the vessel on the receptacle member.